Chip-type solid electrolytic capacitors as shown in FIG. 6 are well known (see JP 2001-6978A).
A solid electrolytic capacitor (1) is provided with a capacitor element (2), to a bottom surface of which is attached a lead frame (9), (90), the capacitor element (2) being covered by a housing (70) made of a synthetic resin.
The capacitor element (2) is made by forming a dielectric oxide coating (21) on the surrounding surface of an anode body (20), which is a sintered valve metal member, with a cathode layer (3), a carbon layer (6), and a silver paste layer (60) formed in this order on the dielectric oxide coating (21). Here, the term “valve metal” refers to a metal which forms an extremely compact dielectric oxide coating having durability when treated by electrolytic oxidation. Al (aluminum), Ta (tantalum), Ti (titanium), and Nb (niobium) are such metals.
An anode lead (22), which is an elongated tantalum cylinder, protrudes from a vertically central portion of the anode bodies (20). The anode lead (22) and the anode-side lead frame (9) have different heights, and are therefore connected electrically via a cylindrical bolster member (4) positioned on the anode-side lead frame (9). A surrounding surface of the bolster member (4) abuts the anode lead (22) and the anode lead frame (9).
The diameter and length of the anode lead (22) are both 1 mm or lower, so bending and attaching the anode lead (22) directly to the anode-side lead frame (9) is difficult. Accordingly, the bolster member (4) is used for the electrical connection of the anode lead (22) and the anode-side lead frame (9).
The following is a manufacturing process for the solid electrolytic capacitor (1). First, as shown in FIG. 7, a metal plate (8) made of copper, steel alloy, or another material is punched and formed such that a terminal component portion (80), which becomes the anode-side lead frame (9), and a terminal component portion (81), which becomes a cathode-side lead frame (90), are separated from one another.
Next, as shown in FIG. 8, the bolster member (4) is placed on the anode-side terminal component portion (80), and that anode-side terminal portion (80) and the bolster member (4) are resistance-welded together. The bolster member (4) is made of tantalum and has a diameter of approximately 0.2 to 0.5 mm and a length of 1 mm or less, and a voltage of approximately 4V is applied with a current of 0.5 kA (electric energy of approximately 2 KJ) when resistance-welding the metal plate (8) made of copper and the bolster member (4).
Next, the capacitor element (2) on which the dielectric oxide coating (21), the cathode layer (3), and so on are formed, are positioned straddling the terminal component portions (80) and (81), and the anode lead (22) and the bolster member (4) are resistance-welded together. As shown in FIG. 9, the capacitor element (2) and the terminal component portions (80) and (81) are covered by a resin which forms the housing (70), forming a resin block (7). This resin block (7) and the terminal component portions (80) and (81) are cut using a dicing saw or similar device along a surface which includes line D—D and line E—E, obtaining the solid electrolytic capacitor (1) shown in FIG. 6.
The following problems exist in making the solid electrolytic capacitor (1).
1. There is variability in the contact area between the bolster member (4) and the anode leads (22) because the surrounding surface of the bolster member (4) abuts the anode leads (22) in a so-called “point contact” manner. Welding is difficult if that contact area is small, as the flow of current when performing a resistance weld deteriorates.
2. Handling of the bolster member (4) is difficult, as it rolls around and gets lost easily, because its diameter and length are both 1 mm or lower and its shape is cylindrical. Consequently, it is difficult and labor-intensive to position the bolster member (4) on the terminal component portion (80) while resistance-welding the terminal component portion (80) and the bolster member (4) together.
3. As shown in FIG. 10, in the above manufacturing method, probes (5) are applied to the terminal component portion (80) and the bolster member (4) and resistance welding is performed, after which, as shown in FIG. 11, the anode lead (22) and the bolster member (4) are resistance-welded. As a result, a welding current is applied twice to the terminal component portion (80).
Consequently, spot defects are more likely to appear on a rear surface of the terminal component portion (80) during welding. The terminal component portion (80) becomes the anode-side lead frame (9), so, as shown in FIG. 6, if the spot defects stand out, this adversely affects the appearance of the solid electrolytic capacitor (1), since the rear surface of the lead frame (9) is exposed. Furthermore, applying the welding current twice to the terminal component portion (80) makes it more likely for the terminal component portion (80) to become deformed due to heat from the current.
An object of the present invention is to resolve the above problems.